1. Field of the Invention
The present invention relates to a vibration resistant vehicle light bulb applied to automobiles and other types of vehicles.
2. Description of Background Art
FIG. 18 illustrates a side view of a conventional automobile light bulb referred to as "H4," wherein the automobile light bulb 100 comprises a glass bulb 101, a cap 102 that seals off the opening of the glass bulb 101, a common lead 103, a cupped shield 104 secured by welding to the top of this common lead 103, a dipped beam filament 105 disposed along this shield 104, a lead 106 for the use thereof, a main beam filament 107 disposed below shield 104, a lead 108 for the use thereof, and a reinforcing bridge 109, a halogen gas is sealed inside glass bulb 101. One leg 105a of the dipped beam filament 105 is affixed to the shield 104, and the other leg 105b is affixed to lead 106.
The three leads 103, 106 and 108 project from cap 102 in the form of cantilever beams, so that these leads 103, 106 and 108 vibrate more toward the tip (the top end) when they are subjected to vibration. Shield 104, which is even further away from cap 102, has a large vibration amplitude, and unless shield 104 is securely welded to common lead 103, the vibration of shield 104 will be delayed with respect to that of the common lead 103 so that when the vibration amplitude increases, the stress in the dipped beam filament 105 disposed along it will increase and its life will become shortened as a result. Unexamined Published Japanese Utility Model Application (JP-A-U) No. S64-2356 (1989) was therefore proposed to combat this problem. The proposed light bulb is described as follows.
FIG. 19 shows a side view of a conventional vibration resistant automobile light bulb, wherein the automobile light bulb 110 comprises a glass bulb 111, a cap 112 that seals off the opening of the glass bulb 111, a common lead 113 whose tip reaches the neck part 111a of the glass bulb 111, a cupped shield 114 that is secured by welding to the mid-part of this common lead 113, a dipped beam filament 115 disposed along this shield 114, a lead 116 for the use thereof, a main beam filament 117 disposed below the shield 114, a lead 118 for the use thereof, and a reinforcing bridge 119, a halogen gas being sealed inside glass bulb 111. One leg 115a of dipped beam filament 115 is affixed to shield 114, and the other leg 115b is affixed to lead 116.
Since the common lead 113 is a beam supported at both ends when its tip is fixed to neck part 111a, its flexion is markedly less than that of a cantilever beam, and its vibration amplitude is also small. The life of dipped beam filament 115 is thus greatly prolonged.
Thus, light bulb 110, which comprises lead 113 linked to glass bulb 111, is called a vibration-resistant automobile light bulb.
FIG. 20 illustrates a cross section taken along line 20--20 in FIG. 19, wherein a cupped shield 114 is affixed by projection welding to common lead 113. More specifically, a small projection is formed from the metal shield 114 to the right of the figure, this projection is brought into contact with common lead 113, and an electrical current is made to flow, causing the electrical current to concentrate at the projection which is welded by the resulting Joule heat. FIG. 21 is a view along arrow 21 in FIG. 19, showing how one leg 115a of dipped beam filament 115 is fixed to cupped shield 114 and the other leg 115b is fixed to lead 116. As this figure illustrates, dipped beam filament 115 is formed from a coil spring of heating wire, pulled out by a distance L in a tangential direction at the end part 115c of the coil, and is then bent up to make a conventional leg structure.
In FIG. 20, there is a danger that the shield 114 will vibrate as shown by the circled arrows 1 centered on the welding point 121. If this happens, it would be inconvenient because dipped beam filament 115, which is attached at one end to lead 116 and at the other end to shield 114 will also vibrate.
Also, in FIG. 21, because leg 115a is separated by a distance L from the center of the glass bulb 111, it is also inconvenient in that leg 115a vibrates along with the vibration of shield 114.